A composition containing at least water as a solvent (aqueous composition) is widely used as a drug, a quasi drug, or the like, because of its advantage of having less stimulation in vivo, or being capable of incorporating various components, for example.
Such an aqueous composition, however, has the problem of being susceptible to microbial contamination due to the inclusion of water. In particular, in the case of a dosage form such as an eye drop, a nasal drop, or an ear drop, which is typically repeatedly used, even if a sterilized container or the like is filled with the aqueous composition, it is brought into contact with non-sterile outside air each time of use, which increases the risk of microbial contamination.
Thus, the aqueous composition is typically provided with an antiseptic effect by incorporating an antiseptic (antimicrobial agent) therein. As the antiseptic, a paraben or a quaternary ammonium surfactant such as benzalkonium chloride, for example, is used.
It has been indicated, however, that this antiseptic has a problem such as cytotoxicity (Non Patent Literature 1, for example), and the use of the aqueous composition as an eye drop, for example, may possibly cause corneal injury; therefore, it is desired to minimize the amount of the antiseptic used as much as possible.
In view of this, establishment of a formulation of an aqueous composition having an excellent antiseptic effect through synergistic action of a combination of a plurality of components would enable a corresponding decrease in the amount of each of the antiseptics used alone, and hence, would enable an aqueous composition having higher safety to be provided.
It is known that halogenated isoquinoline derivatives such as ripasudil (chemical name: 4-fluoro-5-[[(2S)-2-methyl-1,4-diazepan-1-yl]sulfonyl]isoquinoline) represented by the following structural formula:

and 4-bromo-5-[[(2S)-2-methyl-1,4-diazepan-1-yl]sulfonyl]isoquinoline represented by the following structural formula:

which have pharmacological action such as Rho kinase inhibitory action (Patent Literatures 1 and 2, for example), have been reported to be useful, for example, as a prophylactic or therapeutic agent for ocular hypertension, glaucoma, and the like (Patent Literature 3, for example), or as a prophylactic or therapeutic agent for ocular fundus diseases such as age-related macular degeneration and the like (Patent Literature 4, for example), and have also been reported as being prepared as an aqueous composition such as an eye drop composition or the like (Patent Literature 3, for example).
However, antiseptic effects of these halogenated isoquinoline derivatives have thus far never been known.